1. Field of the Invention
The present invention relates to a tower dryer for drying seed cotton, and more particularly relates to a tower dryer having hollow shelves provided with a heated turbulent airflow.
2. Description of the Related Art
Prior to ginning cotton, it is desirable to dry the cotton to remove excess moisture. Foreign matter is more easily removed when the cotton is in a fluffy condition, as usually occurs at five to six percent fiber moisture. At a low moisture content, the ginning process (the separation of the lint from the seed) is also greatly improved.
A tower dryer is frequently used to achieve such drying. In a tower dryer the cotton is exposed to and transported on shelves by a heated airstream. In a typical cotton gin, the seed cotton drying system is the first processing unit, and the cotton is delivered to a duct containing a heated airstream moving at a velocity of 4,000 to 5,000 feet per minute. The conveying air carries the cotton to an exposure chamber, which in this case is a parallel flow tower. The initial exposure of the cotton to heated air results in rapid moisture transfer to the air, resulting in a corresponding cooling of the drying air, due primarily to the cooling effect of evaporation. Initially, when the drying air temperature is high, the drying rate is high. As the air cools, the drying rate drops rapidly. In a conventional tower dryer, adequate drying is difficult to achieve in the few seconds of exposure time. Therefore, it is necessary to repeat the process through additional stages of drying.
In an effort to reduce the number of stages required for drying, it is common to raise the initial mix point temperature for the cotton in the drying air above a safe level, often in the range of 400.degree. F. or higher. The sudden rise in temperature results in varying degrees of damage to the delicate cotton fibers. Fiber damage is becoming increasingly critical due to technological advances in textile mill processing.
It has been discovered that heating the shelves of the tower dryer over which the cotton is moving is desirable to achieve additional drying. Experience has shown that five to six BTU per square foot of surface can be transferred to the drying air for each degree of temperature difference across the shelf surface. U.S. Pat. No. 4,031,593, the disclosure of which is explicitly incorporated herein by reference, describes a relatively efficient tower dryer having heated shelves for drying seed cotton. Nonetheless, it is desirable to further enhance the efficiency of the drying process by increased heat transfer from the heated air to the seed cotton.